The present invention relates to cutting bit holders, especially to holders which support pressed-in replaceable sleeves that carry rotatable cutting bits.
Drum-type cutters are conventional in the mining and road-working industries for example, wherein cutter bits are mounted on a drum which rotates about a horizontal axis. Such cutters can be used to cut through minerals in a mine, or to rip up asphalt or concrete from a roadway. The cutter bits, which are carried by holder blocks welded to the outer surface of the drum, are rotatable about their own longitudinal axes so as to be self sharpening. During a cutting operation, not only do the bits tend to wear, but the holder blocks wear as well. That is, the area of the holder block that surrounds the bit-receiving hole wears due to abrasion thereof by the materials being cut. It will be appreciated that the need to replace the welded-on holder blocks results in a serious expenditure of time and money.
To minimize that problem, it has been proposed to mount each cutter bit in a replaceable hollow sleeve which is inserted into a respective holder block. The sleeve includes a flange that overlies the area of the holder block that surrounds the mouth of the bit-receiving hole, and thereby shields the holder block from appreciable wear. Instead, the sleeves become worn and are replaced when necessary.
One type of such sleeve 10, disclosed in U.S. Pat. No. 5,106,166 and depicted herein in FIG. 1, includes a cylindrical shank 12 that is received in a cylindrical open-ended hole 14 of a holder block 16 that is to be mounted on any suitable carrier 17, such as a rotary drum or an endless chain (e.g., trench digger), or even a non-rotatable carrier. The sleeve is hollow, in order to receive a cutter bit 18 that is mounted in the sleeve for rotation relative thereto by a retainer, e.g., a split sleeve (not shown), that fits within a groove 20 of the bit. The sleeve 10 is held within the hole 14 by a retainer, e.g., a split-ring retainer clip 22 which fits in an external groove 24 of the shank 12. In order to prevent the sleeve from rotating within the holder block, and thus wearing the surface of the hole 14, a key 26 is disposed within aligned recesses formed in a front flange 28 of the sleeve and the holder 16, respectively.
In order to enhance the securement of the sleeve, it has been proposed to mount the sleeve by an interference fit, or press fit. One known type of interference fit comprises a long single cylindrical interference fit. Another type comprises a pair of short cylindrical (or conical) bands of interference fit having different respective cross-sectional sizes (e.g., see U.S. Pat. No. 5,302,005). The provision of such short bands of interference fit is intended to eliminate the need for separate retainers such as split-ring clips and anti-rotation keys. Nevertheless, some sleeves still become prematurely dislodged. Moreover, as the sleeve is being inserted, closed spaces are created between the short bands and the hole surface which can become filled with lubricating oil that is used to facilitate the installation of the sleeve. As the sleeve is advanced into the hole, the oil can become trapped and pressurized as the volume of the spaces diminishes, thereby tending to force the sleeve back out of the hole. As the drum rotates during a cutting operation, the cutting forces push the sleeve into the hole during a cutting phase, but then the pressurized oil pushes the sleeve out of the hole when the respective bit moves out of engagement with the material being cut. Such a reciprocating action of the sleeve can produce undesirable wear of the hole surface.
It would be desirable to ensure that the sleeve is not able to be pushed out of the hole by pressurized lubricating oil, as well as to maximize the forces holding the sleeve against axial and rotary movements within the hole in order to prevent dislodgement of the sleeve during operation.